Federal land managers abruptly ended the roundup of cattle on public land in southern Nevada owned by a rancher who has refused to recognize their authority, citing "serious concern" for the safety of employees and the public.

Bureau of Land Management chief Neil Kornze made the announcement Saturday as hundreds of people, including militia members, gathered near the roundup area to protest the removal of hundreds of Cliven Bundy's cattle.

The bureau also released all 400 of the seized cattle. The move came after protesters, some of them carrying handguns and rifles, headed for a corral outside Mesquite in effort to free the animals. The bureau issued a statement saying the cattle were released "due to escalating tensions."

The fight between Bundy and the Bureau of Land Management has widened into a debate about states' rights and federal land-use policy. The bureau revoked Bundy's grazing rights after he stopped paying grazing fees and disregarded federal court orders to remove his animals.

Kornze's announcement came after Bundy repeatedly promised to "do whatever it takes" to protect his property and after a string of raucous confrontations between federal agents and his family members and supporters during the weeklong operation.

"Based on information about conditions on the ground and in consultation with law enforcement, we have made a decision to conclude the cattle gather because of our serious concerns about the safety of employees and members of the public," Kornze said in a statement.

Bundy did not respond to requests for comment.

Nevada Gov. Brian Sandoval issued a statement praising the agency for its willingness to listen to the state's concerns. The Republican earlier criticized the agency for creating "an atmosphere of intimidation" and trying to confine protesters to a fenced-in "First Amendment area" away from the roundup area.

The 400 cows were gathered during the roundup that began a week ago, short of the BLM's goal of 900 cows that it says have been trespassing on U.S. land without grazing permits for over 20 years.

Bundy, 67, doesn't recognize federal authority on land he insists belongs to Nevada. His Mormon family has operated the ranch since the 1870s.